1. Field of the Invention
The present invention relates to a thin film magnetic head mounted on, for example, a hard magnetic disk device, or the like, and particularly to a thin film magnetic head adaptable to higher recording densities, and a method of manufacturing the same.
2. Description of the Related Art
A thin film magnetic head mounted on a hard magnetic disk device or the like is formed on a slider 51 comprising ceramic such as Al2O3xe2x80x94TiC or the like, as shown in FIG. 21. The slider 51 has a substantially rectangular shape, and comprises one end surface 51a on which the thin film magnetic head is formed, and the magnetic disk-facing surface 51b substantially perpendicular to the end surface 51a. 
A conventional thin film magnetic head is a combination thin film magnetic head comprising a reproducing head h51 and a recording head h52, for example, as shown in FIG. 22. The reproducing head h51 comprises a lower shield layer 52 comprising a soft magnetic film of a Nixe2x80x94Fe alloy or the like formed on an underlying layer 65 made of alumina or the like, a lower gap layer 53 comprising a nonmagnetic material such as alumina or the like and formed to cover the lower shield layer 52, a magnetoresistive element 54 formed on the lower gap layer 53, an electrode layer 55 electrically connected to the magnetoresistive element 54, an upper gap layer 56 comprising a nonmagnetic material such as alumina or the like and formed to cover the magnetoresistive element 54 and the electrode layer 55, and an upper shield layer 57 comprising a soft magnetic Nixe2x80x94Fe alloy film and formed on the upper gap layer 56. In the reproducing head h51, the gap between the upper shield layer 57 and the lower shield layer 52 serves as reproducing gap G1.
In the combination type thin film magnetic head, the recording head h52 comprises a lower core layer also used as the upper shield layer 57 of the reproducing head h51, a gap layer 58 comprising a nonmagnetic material such as alumina, SiO2, or the like and formed on the lower core layer, a coil layer 59 comprising a good conductive material such as Cu or the like and formed on the gap layer 58, and an upper core layer 60 comprising a soft magnetic film of a Nixe2x80x94Fe alloy and formed on the coil layer 59 with an insulating film 61 of resist or the like provided therebetween. The base end 60a of the upper core layer 60 is magnetically connected to the lower core layer serving as the upper shield layer 57.
In the method of manufacturing the conventional thin film magnetic head, the method of producing the upper shield layer 57 comprising a Nixe2x80x94Fe alloy film comprises the underlying film forming step of forming a Nixe2x80x94Fe alloy underlying film to a thickness of 0.1 xcexcm on the upper gap layer by sputtering deposition, and then the plating step of plating an Nixe2x80x94Fe alloy film of about 3 xcexcm thick on the underlying film by an electroplating method using the underlying film as a cathode. In the plating step, the magnitude of the current applied to a plating bath is kept at 7 mA/cm2.
During a drive of the hard magnetic disk device, the slider 51 flies with the magnetic disk-facing surface 51 facing the rotating magnetic disk.
In the reproducing head h51 of the thin film magnetic head, the magnetoresistive element 54 detects a recording signal magnetic field of the magnetic disk, which is produced in the reproducing gap G1 to reproduce a recording signal.
In the combination type thin film magnetic head, the recording head h52 provided on the reproducing head h51 supplies a recording signal to the magnetic disk by means of a leakage magnetic field between the core layers 57 and 60, which is produced by a recording current of the coil layer 59.
At this time, the upper shield layer 57 and the lower shield layer 52 play the function to cut off an extra magnetic field (a magnetic field of a recording signal outside the reproducing gap G1 of the magnetic disk) flowing into the reproducing head h51 from the magnetoresistive element 54.
The upper shield layer 57 is required to prevent a magnetic disturbance from occurring due to a magnetic field from a recording signal of the magnetic disk, a magnetic field induced by the lower core layer of the recording head h52, or deformation due to the head generated from the coil layer 59 or the like, and to have low magnetostriction.
A graph of FIG. 23 indicates that magnetostriction of a Nixe2x80x94Fe alloy film depends upon the composition ratio of the Nixe2x80x94Fe alloy film, and magnetostriction is substantially zero when the Fe composition ratio of the Nixe2x80x94Fe alloy film is close to 18% by weight.
With the Nixe2x80x94Fe alloy film comprising a Nixe2x80x94Fe alloy underlying film formed by sputtering deposition, and a Nixe2x80x94Fe alloy plating film formed by electroplating using the underlying film as a cathode like the upper shield layer 57, the composition ratio of the Nixe2x80x94Fe alloy film depends upon the density of the current applied to the plating bath used in the step of forming the Nixe2x80x94Fe alloy plating film.
FIG. 24 is a graph showing the relation between the current density applied to the plating bath and the composition ratio (Fe % by weight) of the Nixe2x80x94Fe alloy film when the underlying film of the Nixe2x80x94Fe alloy film has a thickness of 0.1 xcexcm, and the plating film has a thickness of about 3 xcexcm.
This graph indicates that the Fe composition ratio of the Nxe2x80x94Fe alloy film is 17 to 19% by weight when the magnitude of the current applied to the plating bath is 6 to 8 mA/cm2.
However, a recent thin film magnetic head in which the reproducing gap G1 has been narrowed with increasing recording density has the problem of producing noise in a reproduced signal of the magnetoresistive element 54 possibly due to magnetostriction of the upper shield layer 57.
FIG. 26 is a graph showing the results of measurement of the Fe composition ratio distribution of the Nixe2x80x94Fe alloy film in the thickness direction thereof with respect to the upper shield layer 57. The graph of FIG. 26 indicates that even when the Fe composition ratio of the entire upper shield layer 57 of about 3 xcexcm is 18% by weight, the plating film having a thickness of about 0.2 xcexcm from the surface of the underlying film is a layer (Fe-rich layer) having a Fe composition ratio of over 19% by weight. As shown in the graph of FIG. 25, the magnetostriction of the Fe-rich layer reaches 2xc3x9710xe2x88x926.
The possible cause of producing noise in the reproduced signal of the magnetoresistive element 54 is that the magnetoresistive element 54 comes near the upper shield layer 57 with narrowing of the gap of the thin film magnetic head, and thus the magnetoresistive element 54 is affected by a magnetic disturbance produced in the Fe-rich layer of the upper shield layer 57.
In the formation of the Nixe2x80x94Fe alloy film by sputtering deposition, the above-described Fe-rich layer is not present, but patterning of the sputtered film requires a dry etching step, and the time required for the dry etching step increases as the thickness of the sputtered film increases to deteriorate etching controllability.
When the whole upper shield layer 57 is formed by the sputtering deposition method, the excessive Nixe2x80x94Fe alloy film is completely removed in the step of patterning the upper shield layer. In this case, the upper gap layer 56, which is thinned due to gap narrowing, is also removed to damage the exposed electrode layer 55.
Accordingly, it is an object of the present invention to provide a thin film magnetic head causing no noise in a reproduced signal due to magnetostriction of an upper shield layer, and adaptable to higher recording densities.
A thin film magnetic head of the present invention comprises a lower shield layer comprising a soft magnetic film, a magnetoresistive element formed on the lower shield layer with a lower gap layer formed therebetween and made of a nonmagnetic material, an electrode layer electrically connected to the magnetoresistive element, an upper gap layer made of a nonmagnetic material and formed to cover the magnetoresistive element and the electrode layer, and an upper shield layer formed on the upper gap layer and opposed to the lower shield layer with the magnetoresistive element provided therebetween, wherein the upper shield layer comprises a Nixe2x80x94Fe alloy underlying film formed on the upper gap layer by sputtering deposition, and a Nixe2x80x94Fe alloy plating film formed on the underlying film by electroplating, and the Fe composition ratio distribution of the upper shield layer in the thickness direction ranges from 17% by weight to 19% by weight.
In this thin film magnetic head, the upper shield layer plays the function to cut off an extra magnetic field from the magnetoresistive element together with the lower shield layer. The upper shield layer has a thickness enough for cutting off a magnetic field by the plating film, and thus the underlying film formed by sputtering deposition may be thin.
In patterning the upper shield layer, the dry etching step is required only for the thin underlying film, and thus the time required for the dry etching step is short, thereby improving etching controllability and preventing the upper gap layer from being deeply cut even when the extra underlying film is completely removed. Therefore, even when the upper gap layer of the thin film magnetic head is thinned with increasing recording density, the electrode layer is not exposed from the upper gap layer in the dry etching step, thereby preventing a damage to the electrode layer.
The Fe composition ratio of the upper shield layer has a distribution in the thickness direction ranging from 17% by weight to 19% by weight.
The magnetostriction of the upper shield layer comprising the Nixe2x80x94Fe alloy film depends upon the composition ratio of the Nixe2x80x94Fe alloy film, and the magnetostriction distribution in the thickness direction lies in the narrow range from xe2x88x922xc3x9710xe2x88x926 to 5xc3x9710xe2x88x927 when the distribution of the Fe composition ratio in the thickness direction ranges from 17% by weight to 19% by weight. It is thus possible to securely prevent the occurrence of a magnetic disturbance from the upper shield layer due to the magnetostriction of the upper shield layer, and obtain a reproduced signal without noise even in a magnetoresistive element which comes near the upper shield layer as the recording density of the magnetic disk increases.
When a layer (Fe-rich layer having a Fe composition ratio of over 19% by weight is present in the Nixe2x80x94Fe alloy film in the thickness direction of the upper shield layer, noise occurs accompanying a discontinuous change in the magnetic domain in the saturation step of a magnetic field induced by the upper shield layer because the magnetostriction of the Fe-rich layer exceeds 0.5xc3x9710xe2x88x926. In addition, the stress of the upper shield layer is liberated on the magnetic disk-facing surface side, and thus a change in stress of the upper shield layer orients the easy magnetization axis of the upper shield layer in the height direction (perpendicular to the magnetic disk-facing surface) to cause a change in the magnetic domain (movement of the magnetic domain wall) of the upper shield layer with an external magnetic field, thereby causing Barkhausen noise. With respect to the change in stress due to the liberation on the magnetic disk-facing surface side, the magnetostriction of the upper shield layer is controlled to zero or slightly minus to stabilize the easy magnetization axis in the track direction (the direction perpendicular to the height direction), thereby advantageously resolving the Barkhausen noise. However, when the magnetostriction is controlled to the minus side from xe2x88x922xc3x9710xe2x88x926, i.e., the Fe composition ratio of the Nixe2x80x94Fe alloy film is controlled to less than 17% by weight, noise occurs due to magnetostriction.
In the thin film magnetic head of the present invention, the thickness of the underlying film is 0.01 to 1 xcexcm.
In the thin film magnetic head, the underlying film plays the function as a cathode for applying a current to the plating bath in the electroplating step of forming the Nixe2x80x94Fe alloy film. With the underlying film having a thickness of less than 0.01 xcexcm, the underlying film has high resistance and many pinholes, causing difficulties in using as the cathode in the plating step.
With the underlying film having a thickness 1 xcexcm or more, a long time is required for the dry etching step for patterning the upper shield layer to deteriorate etching controllability, and the upper gap layer is thus cut in the etching dry step to expose the electrode layer, thereby causing a damage to the electrode layer.
The thickness of the underlying film is preferably 0.06 to 0.2 xcexcm. With an underlying film thickness of 0.06 xcexcm or more, the underlying film can be uniformly formed by sputtering deposition with no variation in the in-plane thickness. Therefore, in the plating step using the underlying film as the cathode, the plating film can be uniformly formed without variations in the in-plane thickness and in-plate composition ratio because of the uniform in-plate potential of the underlying film.
With an underlying film thickness of 0.2 xcexcm or less, the dry etching controllability in patterning of the upper shield layer is further improved, thereby facilitating control of the dry etching step. Furthermore, the time for deposition of the underlying film and the time for the dry etching step for patterning the upper shield layer can be shortened.
The thin film magnetic head of the present invention further comprises a lower core layer also serving as the upper shield layer, a gap layer comprising an insulating material and formed to cover the lower core layer, a coil layer comprising a good conductor and formed on the gap layer, and an upper core layer comprising a soft magnetic film and opposed to the lower core layer with the coil layer provided therebetween.
In the thin film magnetic head, the distribution of magnetostriction of the upper shield layer in the thickness direction ranges from xe2x88x922xc3x9710xe2x88x926 to 5xc3x9710xe2x88x927, and thus no magnetic disturbance occurs from the upper shield layer due to deformation of the upper shield layer due to the heat produced by the coil layer, or a magnetic field induced in the upper shield layer also used as the lower core layer, thereby obtaining a reproduced signal without noise from the magnetoresistive element.
The method of manufacturing a thin film magnetic head of the present invention produces a thin film magnetic head comprising a magnetoresistive element, an upper gap layer comprising a nonmagnetic material and formed to cover the magnetoresistive element, and an upper shield layer opposed to the magnetoresistive element with the upper gap layer provided therebetween, wherein the Fe composition ratio distribution of the upper shield layer in the thickness direction ranges from 17% by weight to 19% by weight. The method of producing the upper shield layer comprises the underlying film forming step of forming a Nixe2x80x94Fe alloy underlying film on the upper gap layer by sputtering deposition, and the plating step of forming a Nixe2x80x94Fe alloy plating film on the underlying film by electroplating using the underlying film as a cathode, wherein the plating step comprises the initial step of forming the Nixe2x80x94Fe alloy plating film on the surface of the underlying film, and the main step of further forming a plating film on the plating film formed in the initial step with the lower current than that applied to the plating bath in the initial step, the initial current density applied to the plating bath in the initial step ranging from 9 to 60 mA/cm2.
In the method of manufacturing the thin film magnetic head, in the plating step of the method of producing the upper shield layer, a high current (initial current) is applied to the plating bath to accelerate discharge of Ni ions in the initial step of forming the Nixe2x80x94Fe alloy plating film on the surface of the Nixe2x80x94Fe alloy underlying film formed by sputtering deposition, thereby suppressing the initial abnormality that Fe is preferentially deposited near the surface of the underlying film.
Since the initial abnormality is relieved by growth of the plating film, in the main step after the initial abnormality relieved by the plating film formed in the initial step, the current applied to the plating bath is decreased to form the upper shield layer comprising the Nixe2x80x94Fe alloy film having a uniform composition ratio (magnetostriction) in the thickness direction thereof.
With the initial current density higher than the current applied to the plating bath in the main step and less than 9 mA/cm2, the effect of preventing the initial abnormality is not obtained, and Fe is preferentially deposited on the surface of the underlying film to produce a layer (Fe-rich layer) having a high Fe composition ratio, i.e., high magnetostriction, near the underlying film. The presence of the Fe-rich layer in the upper shield layer causes noise in the reproduced signal of the magnetoresistive element due to a magnetic disturbance caused by the Fe-rich layer. In order to obtain the sufficient effect of preventing the initial abnormality, the initial current density is preferably 15 mA/cm2 or more.
With the initial current density of over 60 mA/cm2, the load applied to the Nixe2x80x94Fe alloy underlying film used as the cathode is increased, causing difficulties in maintaining the uniformity in the in-plane thickness and the in-plane composition ratio of the plating film.
Since the in-plane thickness and in-plane composition ratio of the plating film tend to become more uniform as the current density applied to the plating bath decreases, the initial current density is preferably 35 mA/cm2 or less.
In the step of producing the upper shield layer, the upper shield layer can be formed so that the magnetostriction distribution in the thickness direction ranges from xe2x88x922xc3x9710xe2x88x926 to 5xc3x9710xe2x88x927. With the upper shield layer having such small magnetostriction, no magnetic disturbance occurs from the upper shield layer, thereby obtaining a reproduced signal without noise in the magnetoresistive element which comes near the upper shield layer as the recording density of the magnetic disk increases.
In the method of manufacturing the thin film magnetic head of the present invention, the plating film formed in the initial step has a thickness of 0.04 to 0.15 xcexcm.
In the manufacturing method, the initial step is changed to the main step at the same time as removal of the initial abnormality to form the Nixe2x80x94Fe alloy plating film having a uniform Fe composition ratio distribution in the thickness direction, i.e., a uniform magnetostriction distribution.
Where the plating film formed in the initial step has a thickness of less than 0.04 xcexcm, the initial abnormality is not sufficiently removed in the initial stage of the main step to form a layer (Fe-rich layer) having a high Fe composition ratio, i.e., magnetostriction shifted to the plus side, in the initial stage of the main step in some cases.
Where the plating film formed in the initial step has a thickness of over 0.15 xcexcm, an excessively high current is applied to the plating bath regardless of the removal of the initial abnormality to form a Ni-rich layer having a high Ni composition ratio in some cases. The Ni-rich layer causes extremely minus magnetostriction or deterioration in soft magnetism.
Furthermore, in the method of manufacturing the thin film magnetic head of the present invention, the current applied to the plating bath in the main step is constant in magnitude.
The manufacturing method can easily control the composition ratio of the Nixe2x80x94Fe alloy plating film formed in the main step, i.e., magnetostriction thereof.
Furthermore, in the method of manufacturing the thin film magnetic head of the present invention, the current applied to the plating bath in the main step is 6 to 8 mA/cm2.
The manufacturing method can securely control the magnetostriction of the plating film formed in the main step in the range of xe2x88x922xc3x9710xe2x88x926 to 5xc3x9710xe2x88x927.
Furthermore, in the method of manufacturing the thin film magnetic head of the present invention, the initial current density is maintained constant.
The manufacturing method can easily control the magnetostriction of the plating film formed in the initial step.
In the method of manufacturing the thin film magnetic head of the present invention, more preferably, the initial current density is 27 to 37 mA/cm2 when the thickness of the underlying film is 0.05 xcexcm, and when the thickness of the underlying film is less than 0.05 xcexcm and over 0.05 xcexcm, the initial current density is higher and lower, respectively, than that with the thickness of 0.05 xcexcm.
In the method of manufacturing the thin film magnetic head, the initial current density is set depending upon the thickness of the underlying film. In the use of the thick underlying film as the cathode in the plating step, the initial abnormality can be prevented even with a low initial current density. Even when the thin underlying film is used as the cathode in the plating step, the initial abnormality can be prevented by increasing the initial current density.
This is possibly due to the fact that as the thickness of the underlying film decreases, the electric resistance decreases to lower the surface potential of the underlying film, thereby preventing the initial abnormality. Therefor, when the thick underlying film is used as the cathode in the plating step, with a high initial current density like in the use of the thin underlying film, the Ni composition ratio is increased due to the application of an excessive current to cause extremely negative magnetostriction or deterioration in soft magnetism in some cases.
With the large current applied to the plating bath, the in-plane thickness and in-plane composition ratio of the plating film are liable to become nonuniform due to the occurrence of variations in the in-plane surface potential of the underlying film. The in-plane surface potential distribution of the underlying film is affected by the in-plane thickness distribution of the underlying film. Therefore, an increase in the thickness of the underlying film can make the in-plate thickness distribution of the underlying film uniform without variations.
Therefore, it is rather advantageous to use the thick underlying film to decrease the initial current density, preventing the initial abnormality. However, the use of the excessively thick underlying film increases the time for the process for producing the upper shield layer, and causes the upper gap layer to be cut in the dry etching step for patterning the upper shield layer, causing damage to the electrode layer. Therefore, the initial current density is preferably 15 to 35 mA/cm2, and the thickness of the underlying film is preferably 0.06 to 0.2 xcexcm.
The method of manufacturing a thin film magnetic head of the present invention produces a thin film magnetic head comprising a magnetoresistive element, an upper gap layer comprising a nonmagnetic material and formed to cover the magnetoresistive element, and an upper shield layer comprising a Nixe2x80x94Fe alloy film and opposed to the magnetoresistive element with the upper gap layer provided therebetween, wherein the Fe composition ratio distribution of the upper shield layer in the thickness direction ranges from 17% by weight to 19% by weight. The method of producing the upper shield layer comprises the underlying film forming step of forming a Nixe2x80x94Fe alloy underlying film on the upper gap layer by sputtering deposition, and the plating step of forming a Nixe2x80x94Fe alloy plating film on the underlying film by electroplating using the underlying film as a cathode, wherein the plating step comprises the initial step of forming a Nixe2x80x94Fe alloy plating film on the surface of the underlying film while increasing the current applied to the plating bath to form the plating film with different current values, and the main step performed after the initial step while maintaining the current applied to the plating bath constant.
In the method of manufacturing the thin film magnetic head, in the plating step of the method of producing the upper shield layer, the current applied to the plating bath is increased in the initial step of forming the Nixe2x80x94Fe alloy plating film on the surface of the Nixe2x80x94Fe alloy underlying film formed by sputtering deposition, thereby suppressing the initial abnormality that Fe is preferentially deposited near the surface of the underlying film without the high current applied to the plating bath. This is possibly due to the fact that by increasing the current applied to the plating bath in the initial step, the effect of accelerating discharge of Ni ions is obtained like in the case in which the high current is applied to the plating bath.
Since the initial abnormality changes with growth of the plating film, the composition ratio of the plating film in the thickness direction thereof can be made further uniform by controlling the rising rate of the current applied to the plating bath. In this case, the current applied to the plating bath is low, and the growth rate of the plating film is high, as compared with the method of suppressing the initial abnormality by applying the high current to the plating bath. Therefore, rigorous precision is not required for controlling the rising rate of the current. In addition, since the current applied to the plating bath is low, the in-plate thickness and in-plate composition ratio of the plating film can be made further uniform.
In the main step after the initial abnormality is removed, the current applied to the plating bath is maintained constant to form the upper shield layer comprising the Nixe2x80x94Fe alloy film having a uniform composition ratio (magnetostriction) in the thickness direction thereof.
In the step of producing the upper shield layer, the upper shield layer can be formed so that the magnetostriction distribution in the thickness direction ranges from xe2x88x922xc3x9710xe2x88x926 to 5xc3x9710xe2x88x927. Since the upper shield layer having such small magnetostriction causes no magnetic disturbance due to magnetostriction, a reproduced signal without noise due to magnetostriction of the upper shield layer can be obtained in the magnetoresistive element which comes near the upper shield layer as the recording density of the magnetic disk increases.
In the method of manufacturing the thin film magnetic head of the present invention, the current applied to the plating bath in the main step is 6 to 8 mA/cm2.
The manufacturing method can securely control the magnetostriction of the plating film formed in the main step in the range of xe2x88x922xc3x9710xe2x88x926 to 5xc3x9710xe2x88x927.
The method of manufacturing a thin film magnetic head of the present invention produces a thin film magnetic head comprising a magnetoresistive element, an upper gap layer comprising a nonmagnetic material and formed to cover the magnetoresistive element, and an upper shield layer comprising a Nixe2x80x94Fe alloy film and opposed to the magnetoresistive element with the upper gap layer provided therebetween, wherein the Fe composition ratio distribution of the upper shield layer in the thickness direction ranges from 17% by weight to 19% by weight. The step of producing the upper shield layer comprises the underlying film forming step of forming a Nixe2x80x94Fe alloy underlying film on the upper gap layer by sputtering deposition, and the plating step of forming a Nixe2x80x94Fe alloy plating film on the underlying film by electroplating using the underlying film as a cathode, wherein the plating step has a delay time between the application of a current to the plating bath and the start of stirring of the plating bath.
In the method of manufacturing the thin film magnetic head, in the plating step of the step of producing the upper shield layer, the delay time in which the plating bath is not stirred is provided between the application of a current to the plating bath and the start of stirring of the plating bath so that the Nixe2x80x94Fe alloy plating film is formed on the surface of the underlying film without stirring the plating bath during the delay time, thereby preventing the initial abnormality that Fe is preferentially deposited near the surface of the underlying film.
The initial abnormality is removed with the growth of the plating film, and stirring of the plating bath is started after the predetermined delay time to form the Nixe2x80x94Fe alloy film having uniform magnetostriction (Fe composition ratio) in the thickness direction.
In the step of producing the upper shield layer, the upper shield layer can be formed so that the magnetostriction distribution in the thickness direction ranges from xe2x88x922xc3x9710xe2x88x926 to 5xc3x9710xe2x88x927. Since the upper shield layer having such small magnetostriction causes no magnetic disturbance due to magnetostriction, a reproduced signal without noise due to magnetostriction of the upper shield layer can be obtained in the magnetoresistive element which comes near the upper shield layer as the recording density of the magnetic disk increases.
In the method of manufacturing the thin film magnetic head of the present invention, the current applied to the plating bath in the main step is constant in magnitude.
The method of manufacturing the thin film magnetic head has no need to apply a high current to the plating bath in order to prevent the initial abnormality, thereby suppressing variations in the in-plane thickness and in-plane composition ratio of the plating film due to the application of an excessive current. In addition, the current applied to the plating bath need not be changed, simplifying the manufacturing process.
In the method manufacturing the thin film magnetic head of the present invention, the magnitude of the current applied to the plating bath is 6 to 8 mA/cm2, and the delay time is 6 to 9 seconds.
In the method manufacturing the thin film magnetic head, the magnitude of the current applied to the plating bath is 6 to 8 mA/cm2, and thus the magnetostriction distribution of the plating film in the thickness direction, which is formed in the main step, can be controlled in the range of xe2x88x922xc3x9710xe2x88x926 to 5xc3x9710xe2x88x927.
In the method, since the delay time is 6 to 9 seconds, the initial abnormality can be removed within the delay time, and stirring of the plating bath is started at the same time as the removal of the initial abnormality, thereby forming the Nixe2x80x94Fe alloy plating film having a uniform magnetostriction distribution in the thickness direction thereof.
With a delay time of less than 6 seconds, the initial abnormality is not sufficiently removed within the delay time to form a layer (Fe-rich layer) having a high Fe composition ratio, i.e., magnetostriction shifted to the plus side in some cases.
With a delay time over 9 seconds, the initial abnormality is removed, but a Ni-rich layer having a high Ni composition ratio is formed because the plating bath is not stirred in some cases, thereby causing extremely negative magnetostriction in the Ni-rich layer or deterioration in soft magnetism.